Operators aimed to resume mining as early as later in the day, but now estimate it will take until at least the weekend to complete investigations with government regulators into the cause of the contamination.

Operations at the site, 250 km (150 miles) east of Darwin in Australia's far north, ground to a halt on Tuesday when the problem emerged and all non-essential staff sent home, a Rio Tinto spokeswoman said. Government officials were not immediately available to comment.

The number of staff complaining of mild symptoms after showers that may be related to the contaminated water had risen from two to three, Rio Tinto subsidiary Energy Australia Ltd (ERA.AX: Quote, Profile, Research) said in a statement.

The mine and plant employ about 200 workers and is owned by ERA, which is 68.4-percent-owned by Rio Tinto (RIO.L: Quote, Profile, Research) .

'Elevated levels of uranium'

"We are not sure exactly how this has occurred but uranium got into potable water," the spokeswoman said.

It appeared that an erroneous connection was made between the potable water line used for drinking and washing and the water line used in processing the uranium, she said.

The privately run Environment Centre Northern Territory called on government authorities to investigate the incident.

The centre's researchers said the water was found to contain levels of uranium up to 400 times safe drinking levels, but Rio Tinto said it had been assured by health officials that the contamination posed no health risk to workers and that the water supply in the nearby town of Jabiru was not affected.

"This is not a place to cut corners," Peter Robertson, the centre's co-ordinator, said in a statement. The plant treats low-grade uranium oxide which is then stored in barrels before being shipped to North America, Japan and Europe, where it is enriched and used in nuclear power generation.

Staff coming off the night shift complained of a gritty feel and salty taste to water used to shower before going home, the Rio Tinto spokeswoman said.

"The water was tested and found to contain elevated levels of uranium and higher acidity," she said.

ERA shares closed down four percent at A$3.55 and Rio Tinto shares down 1.5 percent at A$33.90 in a flat wider market.

Human error likely cause of Ranger contamination

Sarah Belfield, Miningnews.net

Tuesday, March 30, 2004

A wrong connection between potable and process water systems may have been the cause of the water contamination incident last week at Energy Resources of Australia's Ranger uranium mine, according to the company.

ERA said the connection may have been made before Tuesday night last week, which was when a change in water supplies occurred, according to initial investigations. The company said records from routine water testing indicate no impact on drinking and washing water before Tuesday night.

Australian government supervising scientist Arthur Johnston has also been assessing the impact of a second, associated incident where process water leaked into a creek system nearby.

His understanding is that process water back-flowed into a header tank and then overflowed into the creek, probably occurring on Tuesday night or Wednesday morning.

Johnston announced yesterday that concentrations of all measured chemicals downstream from the mine in Magela Creek have remained within normal ranges, and that no adverse effects have been observed in monitored animals.

Magela Creek feeds a large wetland area, a spokeswoman for Johnston told MiningNews.net.

Johnston will discuss the incident today along with data results in meetings with traditional owners of the area and the broader Jabiru community.

"This problem in addition to the contamination of the potable water supply at the plant is not good enough," Johnston said on Friday.

Last week Johnston requested that ERA not resume Ranger operations until he has complete confidence that systems are in place to prevent a similar incident from happening again.

In April 2002, the federal government warned ERA to lift its game following a report by the supervising scientist into the mismanagement of a low-grade ore stockpile, which occurred in March that year.

From 1979 to January 2004, the supervising scientist assigned a "significant" status to two incidents reported at Ranger. One occurred in 1982 and involved the health and safety of two workers in the packing plant and another took place in 1995, involving a spill of diesel at the power station.

To extract uranium, ore is crushed and then pumped as a slurry to a thickener, where excess water is removed, before heading to leach tanks where sulphuric acid is added to dissolve uranium-bearing minerals.

Solids are removed from the uranium-rich solution and kerosene then selectively strips uranium from the solution. Ammonia precipitates the uranium, which then passes to a furnace where ammonia is driven off, allowing uranium oxide to form.